If there is no Lesson card in your graveyard when Walltop Sentries dies, the ability will not be put on the stack at all
Commander blue-red control Instant (22) 1x AEther Tradewinds 1x Aetherize 1x Blustersquall 1x Bombard 1x Brainstorm 1x Convolute 1x Dissolve 1x Engulf the Shore 1x Essence Scatter 1x High Tide 1x Hornswoggle 1x Hungry Flames 1x Leave in the Dust 1x Magmaquake 1x Mana Leak 1x Mirror Match 1x Mystic Confluence 1x Negate 1x Opt 1x Shock 1x Snap 1x Spell Rupture Enchantment (7) Sorcery (16) 1x Call to Mind 1x Chain Reaction 1x Deja Vu 1x Grasping Current 1x Mizzium Mortars 1x Mizzix's Mastery 1x Mutiny 1x Open Into Wonder 1x Ponder 1x Preordain 1x Pull from the Deep 1x Relearn 1x Rite of Replication 1x River's Rebuke 1x Silent Departure 1x Sleep Land (36) 1x Command Tower 24x Island 1x Izzet Boilerworks 6x Mountain 1x Reliquary Tower 1x Temple of the False God 1x Vivid Crag 1x Vivid Creek Artifact (4) Commander (1) Creature (13) 1x Archaeomancer 1x Arjun, the Shifting Flame 1x Docent of Perfection Flip 1x Gigantoplasm 1x Goblin Electromancer 1x Illusory Ambusher 1x Melek, Izzet Paragon 1x Mizzix of the Izmagnus 1x Protean Raider 1x Psychosis Crawler 1x Siren Stormtamer 1x Talrand, Sky Summoner 1x The Locust God
The most interesting applications come from forcing challenges with cards that gain benefits from being challenged or banished
PhyrexianWombat says
MH3 retro frame cards, including new-to-Modern uncommons (7 commons, 16 uncommons, 24 rares, and 8 mythic rares that show up 4.2% in total) Commander mythic rares (8 cards, both regular and borderless
The payoff of this meld pair, doesn't win the game on the spot, and I'd stress that to your Bracket 3 playgroup because while this deck puts together powerful cards, it is not optimized to be unbeatable, and more focused on a huge play with some Golgari death and graveyard interaction molded in
